Castillo de Monreal de Ariza is a medieval fortress in the municipality of Monreal de Ariza in Zaragoza province, founded by Alfonso I the Battler in 1128 as Mont Regal to consolidate Aragón's advance against the Almoravids and defend the frontier with Castile. Over three centuries, the castle served as a principal fortified post controlling the Jalón River border region. The complex comprises four walled compounds arranged topographically with different elevations, dominated by a main pentagonal tower in ruins at the summit. Within the fortress lies the remains of a Romanesque church dedicated to Our Lady of the Assumption, dating to the 12th-13th centuries and reflecting the castle's role as both military stronghold and spiritual center. Currently owned by the Municipality of Monreal de Ariza, the castle faces progressive ruin but remains an important testament to Aragonese medieval fortification.
